A magneto-optical storage device such as a magneto-optical disk has a configuration wherein, for example, the first dielectric layer, a recording layer, the second dielectric layer, a reflective layer and an overcoat layer are successively laminated on a substrate in this order.
The first and second dielectric layers are made up of, for example, AlN. The film thicknesses of the first and second dielectric layers are respectively arranged so that a light beam such as a laser beam, which has been incident thereon from the substrate side, is reflected with a predetermined reflective index, and so that the Kerr rotation angle of the reflected light beam is maximized. The magneto-optical storage device having the above arrangement is intended to prevent oxidation of the recording layer and to increase the Kerr rotation angle by utilizing the multiple reflection.
Amorphous rare-earth transition-metal alloys such as GdTbFe and TbFeCo are widely used for composing the recording layer. The recording layer is normally set to 15 nm-25 nm in thickness.
On the other hand, in recent years, magneto-optical storage devices provided with a Pt/Co multi-layer film have been recognized as a medium for enabling magneto-optical recording with high density. The Pt/co multi-layer film is constituted by Pt layers and Co layers that are alternately laminated one after the other. As is disclosed in Japanese Laid-Open Patent Application No. 2-263344, the Pt/Co multi-layer film exhibits the perpendicular magnetic anisotropy and provides a larger magnetic Kerr rotation angle with respect to light having a short wavelength than that made of a rare-earth transition-metal alloy.
Here, it is desirable for the Pt/Co multi-layer film to have a high coercive force in order to stably maintain recorded information. Some of those methods for manufacturing a Pt/Co multi-layer film with a high coercive force have been found in the abstracts of technical research reports of Japan Applied Magnetics Institute issued in 1989.
For example, according to a method described on page 55 in the abstracts, it is possible to obtain a Pt/Co multi-layer film with a high coercive force by increasing the pressure of Ar gas, which is used as a sputtering gas, during the manufacturing process of the Pt/Co multi-layer film through the sputtering method.
Moreover, according to a method described on page 56 in the abstracts, it is possible to obtain a Pt/Co multi-layer film with a high coercive force by forming it on a metal film having a fcc (face-centered cubic) structure, such as Pt and Pd, through the sputtering method.
In the case of adopting the aforementioned magneto-optical storage device using a rare-earth transition-metal alloy, since the Kerr rotation angle is greatly dependent on the film thicknesses of the first and second dielectric layers, even a small deviation of the film thickness from an appropriate setting value may decrease the Kerr rotation angle. This results in the problem that it is difficult to manufacture a magneto-optical storage device having stable performance.
Moreover, in the case of adopting the magneto-optical storage device wherein a Pt/Co multi-layer film is employed, the following problems have been encountered. As described in "IEEE TRANSACTIONS ON MAGNETICS", volume 25, number 5, page 3764, published in 1989, if the film thickness ratio between the Pt and Co layers of the Pt/Co multi-layer film (the film thickness of the Pt layer/that of Co layer) is increased, the Kerr rotation angle is conversely decreased, although a stable perpendicular magnetization is obtained. As a result, it is difficult to obtain a Pt/Co multi-layer film that has a stable perpendicular magnetization and also provides a large Kerr rotation angle to the incident light.
Furthermore, as to the manufacturing process of the Pt/Co multi-layer film, when a Pt/Co multi-layer film is produced under such a high pressure of Ar gas, a large number of pores are produced in the Pt/Co multi-layer film. In the case of forming a Pt/Co multi-layer film on a metal film having the fcc structure, if the metal film thickness is increased in order to increase the coercive force, the crystal grains of the Pt/Co multi-layer film are also grown in size. Therefore, when a magneto-optical storage device that has a Pt/Co multi-layer film manufactured through the above methods, is employed, noise might be caused during information reproduction due to the increased number of pores and the largeness of the crystal grains in the Pt/Co multi-layer film.